The Glycosaminoglycans (GAG's) are copolymers of uronic acid and amino hexose with a sequence that has unique biological activity. When prepared from natural sources, this family of heterogeneous macromolecules has sequences that bind specific proteins providing them with various biological activities. Some of the interactions that are of therapeutic utility are between the serine proteases generally and in particular the blood protein anti-thrombin III. This interaction is dependent on special structural sequences that are present in the depolymerized natural product.
The multiplicities of commercially available preparations of heparins are manufactured by diverse processes with variable starting materials yielding products with unique structural components and different biological activities. The commercial products called heparins are thus generally undefined tissue derived panoply of long chain polysaccharides. The structural variability may be a result of the extraction process, the source and condition of the starting materials as well as the collection methods. The resulting biological activities of the product are influenced by these variables.
Heparins are common GAG's made up mainly of D-glucosamine and L-iduronic or D-glucuronic acid sulfated at different sites, having a wide range of molecular weights, and are generally used as anticoagulants and antithrombotic compositions. Low-molecular weight heparins are heterogeneous depolymerized products having a lesser degree of polymerization. The resulting biological properties are a function of polymer chain length and molecular weight distribution. Additionally, the method of preparation of mucosal GAG's yield products with different end groups. One such end group is 2-5 anhydro-D-mannoses, a result of enzymatic depolymerization.
The importance of this class of compounds in clinical medicine is based on its profound action on the coagulation system. Systemic coagulation is an integral part of many diseases and appears as a defense mechanism in trauma. Activation by the coagulation mechanism is a necessary part of the host's immune system. The coagulation system is not only involved in preventing blood loss following trauma, but clotting pathways may be involved in the pathology of allergy and inflammation. Deposits of fibrin surrounding cancer cells may also aid in the progression of growth of malignant tumors. There are multiple other properties of GAG's which are of potential interest as therapeutic agents.
The sequences in the linear GAG polymers that are responsive to the serine protease activity have been chemically synthesized. The natural glycosaminoglycans of interest as well as the synthetic analogs are made up of alternative units of L-iduronic and D-glucuronic acid: D-glucosamino units that are N-sulfated and N-acetylated. The 1-4 linked L-iduronic acids and the D-glucosamino acids have o-sulfate groups.
Although the therapeutic effects of these compounds are well documented, their use is limited because of their poor oral absorption and short half-life. Injectable forms of these compounds exist and efforts have been made to provide an orally absorbable formulation of these compounds. An object of this invention is to provide compositions which are orally absorbable, and thus make them available for a broad spectrum of clinical conditions including cancer.
It has been postulated that the primary cause of death in cancer patients is due to the consequences of metastasis. See Chambers, A. F., A. C. Groom, and I. C. MacDonald, Dissemination and growth of cancer cells in metastatic sites. Nat Rev Cancer, 2002, 2(8): p. 563-72.
Heparin is an efficient anti-metastatic agent; it inhibits metastasis by binding to P-selectin and blocking the adhesion between platelets and the disseminated tumor cells in the blood. The use of heparin as an anti-metastatic agent is limited due to the bleeding side effect.
Metastasis is a cascade of events that starts when some cells escape the primary tumor, survive in the circulatory system, and eventually seed in distal metastasis. Ample evidence supports the concept that blood-borne metastasis is significantly facilitated by interactions between disseminating tumor cells and blood platelets that results in the formation of micro-thrombi. See Nash, G. F., et al., Platelets and cancer. Lancet Oncol, 2002, 3(7): p. 425-30. See Ruiter, D. J., et al., Tumour metastasis: is tissue an issue?, Lancet Oncol, 2001, 2(2): p. 109-12. See Karpatkin, S. and E. Pearlstein, Role of platelets in tumor cell metastases, Ann Intern Med, 1981. 95(5): p. 636-41. See Gasic, G. J., Role of plasma, platelets, and endothelial cells in tumor metastasis, Cancer Metastasis Rev, 1984, 3(2): p. 99-114. See Honn, K. V., D. G. Tang, and Y. Q. Chen, Platelets and cancer metastasis: more than an epiphenomenon, Semin Thromb Hemost, 1992, 18(4): p. 392-415.
Selectins are a family of cell adhesion molecules, and are divided into three groups: E, L and P, which are found on the surface of endothelial cells, leukocytes, and platelets, respectively. Selectins have roles in hemostasis, inflammation, and the immune response. See McEver, R. P., Selectin-carbohydrate interactions during inflammation and metastasis, Glycoconj J, 1997. 14(5): p. 585-91. See Ley, K, The role of selectins in inflammation and disease, Trends Mol Med, 2003, 9(6): p. 263-8.
P-selectin was found to be most relevant in the process of tumor metastasis and has been studied extensively. The adhesions that form between tumor cells and platelets via P-selectin are required to create the metastatic micro-thrombi. See Borsig, L., et al., Heparin and cancer revisited: mechanistic connections involving platelets, P-selectin, carcinoma mucins, and tumor metastasis, Proc Natl Acad Sci USA, 2001, 98(6): p. 3352-7.
The activation of endothelial P-selectin also plays a role in the arrest of circulating tumor cells, and their eventual extravasation from the blood vessel into the distal organs. See Ludwig, R. J., et al., Endothelial P-selectin as a target of heparin action in experimental melanoma lung metastasis, Cancer Res, 2004, 64(8): p. 2743-50.
Sialylated fucosylated glycans are the ligands for P-selectin, and tumors with high expression of these ligands typically have poor prognosis due to high rates of metastasis. See Stone, J. P. and D. D. Wagner, P-selectin mediates adhesion of platelets to neuroblastoma and small cell lung cancer, J Clin Invest, 1993, 92(2): p. 804-13. See Mannori, G., et al., Differential colon cancer cell adhesion to E-, P-, and L-selectin: role of mucin-type glycoproteins, Cancer Res, 1995, 55(19): p. 4425-31.
Heparin was found to be an efficient ligand for P-selectin and blocks the binding of P-selectin with tumor cells, and therefore attenuates tumor metastasis in animal models. See Nelson, R. M., et al., Heparin oligosaccharides bind L- and P-selectin and inhibit acute inflammation, Blood, 1993, 82(11): p. 3253-8. See Koenig, A., et al., Differential interactions of heparin and heparan sulfate glycosaminoglycans with the selectins. Implications for the use of unfractionated and low molecular weight heparins as therapeutic agents, J Clin Invest, 1998, 101(4): p. 877-89.
By depriving the circulating tumor cells their platelet shield, they become more fragile in the harsh environment of the circulatory system and are more readily cleared by the immune system.
Heparin is best known for its anticoagulant properties, because it binds to anti-thrombin III. See Rosenberg, R. D. and P. S. Damus, The purification and mechanism of action of human antithrombin-heparin cofactor, J Biol Chem, 1973, 248(18): p. 6490-505.
Heparin's anti-metastatic properties are a result of one or more of the following: the inhibition of heparenase, the blocking of P- and L-selectins (see Zacharski, L. R. and J. T. Loynes, The heparins and cancer, Curr Opin Pulm Med, 2002, 8(5): p. 379-82)); inhibition of tissue factor (see Kasthuri, R. S., M. B. Taubman, and N. Mackman, Role of tissue factor in cancer, J Clin Oncol, 2009, 27(29): p. 4834-8); and the inhibition of angiogenesis (see Capila, I. and R. J. Linhardt, Heparin-protein interactions, Angew Chem Int Ed Engl, 2002, 41(3): p. 391-412).
Low molecular weight heparin (LMWH) has been shown to decrease tumor metastasis in animal experiments and clinical trials, but the use of heparin and its derivatives as anti-metastatic agents is limited because of its risk in inducing adverse bleeding complications. A meta-analysis performed in 2007 showed an increase in bleeding in patients treated with LMWH as an anti-metastatic medication. See Kuderer, N. M., et al., A meta-analysis and systematic review of the efficacy and safety of anticoagulants as cancer treatment: impact on survival and bleeding complications, Cancer, 2007, 110(5): p. 1149-61.
Tumor excision of a primary cancer with no metastasis has been the cornerstone treatment for most cancers, but scientific evidence has revealed that cancer excisional surgery itself can increase the risk of metastasis. See van der Bij, G. J., et al., The perioperative period is an underutilized window of therapeutic opportunity in patients with colorectal cancer, Ann Surg, 2009, 249(5): p. 727-34.